The only thing I'd add to what Sourdough-Guy has already said is to give you another data point on the amount of starter you use and time.

Most of the time, I use a large amount of starter (30% of the total flour weight), which gives me a bulk fermentation of about 4 hours at room temperature (68 degrees F) and then a final proof of 2 to 2.5 hours at about 85 degrees F.

If I'm doing an overnight sourdough, I'll use about 10% of the total flour weight and let it sit for about 12 hours bulk at room temp and then 3 hours or so at 85 degrees for the final proof.

As for your second question, 50-50 flour to water by weight would be 100 percent hydration. If you're doing it 50-50 by volume it's probably closer to 175% or 200% hydration, depending on whether you've got a light or a heavy hand in packing flour into the measuring cup. One cup of flour weighs anywhere from 4-5 ounces, whereas one cup of water is always around 8 ounces. If you want to get technical, of course, changes in the water temperature alter how much water by weight you can get into a cup, but not enough to mean anything to a home baker, really.

Hydration is measured by taking the weight of the water and then dividing it by the weight of the flour. So if you've got 500 grams of flour and 400 grams of water, you'd have 400/500 which gives you 80% hydration.

The yeast or starter has living cells that multiply over time. When you add yeast or starter, you are starting off with a population of cells in your dough that will multiply and grow from there.

The population of cells in your dough will double in something like 2 hours (very roughly). That means that the difference between putting in, let's say, 1/4 tsp of yeast as opposed to 1 tsp of yeast is that if you put in 1/4 tsp you have to wait a few hours for the population to double twice (i.e. multiply by 4) and end up the same as the population you would have had after adding 1 tsp of yeast.

The idea is the same with starter, except we talk about the percentage of flour contributed by the starter to the total flour weight. Typical amounts are anywhere from 5% to 30% of the TFW is contributed by the flour in the starter.

Given all that, you could imagine mixing a dough at 9:00AM and putting in 1/4 tsp yeast, and mixing another dough at about 1:00PM adding 1 tsp of yeast. Both doughs should be ready for baking at about the same time after that. Similarly you could imagine making a dough with 50 grams of starter at 9:00AM and a dough at around 1:00PM with 200 grams of starter and having those two doughs ready to bake at about the same time.

There are many ways to do it and they all work but I like this simple no-math version best. I find it is easy for beginners to understand.

The easiest way I have found to adapt a recipe without altering the ingredients too much is to take all of the liquid from the recipe, stir in 2 Tbsp. starter, add the same amount of flour as the liquid. Let this sit, covered, overnight (room temp.) Next day, continue by adding the rest of the ingredients, remembering that you already used the liquid and part of the flour. If your recipe calls for milk rather than water, use water but then stir in some dry milk powder after the overnight proofing is complete and then mix your dough.

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